It's a lot of fun if you like battling in giant robots. They billed it as the thinking shooter since you have time to think and react to the battle and they were right. It's in open beta so it still has it's share of crashes to desktops though.

Most importantly: Charging out alone will almost always result in your dying, and your team losing. Call of Duty playstyle is the worst thing you could possibly attempt in this game.

You need to play as a team to win, strategy and tactics count for more than in most other games. More than TF2, more than Battlefield, more than most games that advertise this as a major feature.

You need to manage your aiming separately from your movement, which is the hardest thing to adjust to for most people.

You need to manage 2-5 separate weapons systems, simultaneously, instead of 'switching back and forth' like in other FPS's. This is a lot to mentally deal with. Each weapon will have its own ranges, projectile speed etc, meaning the firing profile changes depending on which gun you're trying to shoot, and you need to shoot all of them at the same time, a lot of the time. For some context, imagine TF2, where you have the heavy's minigun, soldier's rocket launcher, a sniper rifle and and a scout's shotgun, all onscreen at the same time, and each bound to a different mouse button. Each can be fired independently and simultaneously and has its own refire/reload times that don't affect the other weapons.

You aim weapons on your torso separately from your arms, so there are two crosshairs you need to pay attention to simultaneously, which is especially complicated considering the previous note.

You need to manage heat, a concept foreign to most players of FPS's.

You need to know what every mech is capable of equipping, and you need to know what every weapons system does, or you will not be able to prioritize targets in battle properly.

And the mechlab: You build your mech from the ground up, so the amount of customization in the hands of the user almost certainly greater than than any other game you are likely to have seen. This allows you an unreal amount of creative leeway when it comes to how you want to play the game, but it also means your performance is as connected to your builds as it is to your skill in the cockpit

Since Microsoft still owns the rights for battletech video games (they've licensed them to PGI/IGP), I wouldn't hold your breath on seeing a mech game on OSX. That being said, the game is amazingly fun, but it's very much a team based game and takes quite a bit more stratagy than CoD or BF3.